A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgear designed to protect high voltage circuits feeding an entire city.
All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker. Low voltage (less than 1000 VAC) type electrical circuit breakers are common in domestic, commercial and industrial application, and include: miniature and mini circuit breakers (MCBs), mmolded case circuit breakers (MCCBs), residual-current devices (RCDs) and circuit breakers that combine the functions of an RCD with overcurrent protection (RCBOs). Circuit breakers typically comprise a casing or housing molded from thermoplastic or thermoset materials. Some further characteristics of circuit breakers are the following: MCB (Miniature Circuit Breaker)—rated current generally not more than 125 A; trip characteristics are normally not adjustable. MCCB (Molded Case Circuit Breaker)—rated current up to 1000 A, and functioning through thermal or thermal-magnetic operation; trip current may be adjustable in larger ratings. RCDs, MCBs, MCCBs, RCDs and RCBOs have in common that all typically comprise a housing molded from thermoplastic or thermoset materials. MCCBs, RCDs and RCBOs are described for example by K. Kuboyama and A. Kohanawa in Fuji electronic review, Vol. 52, No. 4, pages 112-118.
A circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit. Small circuit breakers may be manually operated (also work with a solenoid for short circuit and a bi-metal for thermal tripping); larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials. Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature and molded case circuit breakers are usually discarded when the contacts are worn, but power circuit breakers and high-voltage circuit breakers have replaceable contacts. When a current is interrupted, an arc is generated. This arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. A high arcing voltage and a high shutting speed are important. Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.
Low voltage circuit breakers typically comprise an arc formation chamber (or arcing chamber) and an arc extinguishing chamber (or arc chute). The arc extinguishing chamber typically comprises a stack of so-called deionizing plates or arc splitter plates, typically made of metal. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms. Different techniques are used to extinguish the arc. Low-voltage circuit breakers comprise an arcing chamber wherein gas generated by the arc is expanded. Miniature low-voltage circuit breakers the arc is extinguished under air. Larger ratings circuit breakers such as some mini-circuit breakers and MCCBs typically contain metal splitter plates, or non-metallic arc chutes to absorb energy, to divide and cool the arc, and reduce the conductivity of the gases. Magnetic blowout coils can be used to deflect the arc into the arc chute.
From the prior art electrical circuit breakers comprising an arc chute equipped with side flanges are known. US 2008/0290068 describes an arc chute comprising an arc extinguishing chamber formed by a stack of deionizing plates and an arc formation chamber bounded by a first and second flange, said arc chute being equipped with permanent magnets arranged behind at least the first flange, in which the arc formation chamber comprises: an enhanced induction section where the arc is propelled towards the arc extinguishing chamber by a first part of the permanent magnets, and a diverting section where the arc is diverted towards the first flange by a second part of the permanent magnets, the magnetic field in the longitudinal mid-plane generated by the second part being substantially weaker than that generated by the first part. The flanges in these electrical circuit breakers are made of isolating material.
U.S. Pat. No. 7,541,902B relates to the field of switchgear devices in particular enabling direct currents to be broken, in particular low-intensity currents, i.e. comprised between 0.5 and 150 Amperes. U.S. Pat. No. 7,541,902B describes a circuit breaker comprising an arc chute for comprising an arc extinguishing chamber formed by a stack of deionizing plates and an arc formation chamber bounded by a first and second flange, said arc chute being equipped with permanent magnets arranged behind at least the first flange. According to one embodiment, the first flange is made of ceramic material, while the second flange is made of gas-generating organic material.
EP1313121A1 describes electrical circuit breakers, comprising an arc-extinguishing member including a molded arc-extinguishing insulating material mainly containing a non-halogenous flame retardant. The non-halogenous flame retardant can be chosen from many different materials including organic triazine compounds, such as melamine cyanurate. The matrix resin in the arc-extinguishing insulating material can be chosen from different materials, including polyamides, such as non-aromatic polyamides.
A problem with low voltage electrical switch gears is their limitation in maximum arc switch voltage that is built up, the switching speed and retention of performance after multiple short circuitry interruptions.
The aim of the invention is to provide an electrical circuit breaker, wherein problems as described above are reduced, at least to some extent.
This aim has been achieved with the electrical circuit breaker according to the present invention, comprising an arc formation chamber being at least partially bounded by a side flange consisting of a flame retardant polymeric composition comprising a thermoplastic polymer, a flame retardant system comprising a triazine based flame retardant and 0-5 wt. % of phosphorous or halogen containing flame retardants, and 0-15 wt. % of a reinforcing agent, wherein thermoplastic polymer comprises a polyamide with a melting temperature of at least 260° C. and the triazine based flame retardant comprises at least 20 wt. % of melam, wherein the weight percentages (wt. %) are relative to the total weight of the composition.